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The concentration of symphytine and echimidine varies between teas prepared from leaves purchased from different vendors.5 Nine of 11 comfrey products available in health food stores were found to contain measurable quantities of one or more alkaloids, in ranges from 0.1 to 400.0ppm.7 The highest levels were found in bulk comfrey root, followed by bulk comfrey leaf, followed by comfrey combination products.

Poly[oxy-1-carboxy-2-(3,4-dihydroxyphenyl)ethylene] was isolated from the roots of Symphytum asperum and Symphytum caucasicum.12 3-O-[beta-D-glucopyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->4)-alpha-L-arabinopyranosyl]-oleanolic acid was isolated from the ethanol-soluble portion of Symphytum officinale roots. 13

Mucopolysaccharides, saponins, allantoin, rosmarinic acid, tannins, and lithospermic acid are also found in comfrey.14,15,16,17,18,19,20,21

Antifungal effects: Extracts from the leaves of comfrey inhibited the germination of Erysiphe graminis conidia and uredospores of Puccinia graminis, resulting in diminished powdery mildew infection of plants.1 It is not clear whether comfrey has clinical antifungal effects.

Immune effects: In an animal study, an aqueous extract obtained from roots of Symphytum officinale initially activated the respiratory burst of macrophages and later activated the synthesis of catalase and superoxide dismutase.23 The clinical significance of this is unknown.

In an animal study, topical application of a crude alcoholic extract resulted in very low absorption of pyrrolidizine alkaloids.24 0.1-0.4% of the dose was recovered in the urine over the next 24 hours.